The present invention relates generally to data and information communications systems and their operation and more particularly to communications networks including a Fibre Channel network. Even more particularly, the present invention relates to a Fibre Channel network system and method of operation having the ability to maintain the target and initiator states across address changes for improving the management of inputs and outputs to improve network performance, eliminate communication failures, and avoid the loss of data that may occur as a result of a network link state change.
In a Fibre Channel network, the network address assigned to initiators and targets may be dynamic. After a link state change on the network, the network addresses assigned to existing nodes in the network can change. This behavior executes a problem for SCSI initiators and targets in managing I/O (inputs/outputs) in progress between a specific initiator-target pair across link state changes.
With known methods for managing I/Os in a Fibre Channel network, when an existing I/O is in progress and either an initiator or target detects a link state change, the initiator must authenticate that it is still talking to the same target before the I/O can continue. This authentication is detailed in The Fibre Channel PLDA (Private Loop Direct Attach) Profile. This profile is an extension to the SCSI-3 Standard FCP (Fibre Channel Protocol), which defines SCSI implementation over Fibre Channel. The PLDA profile states that after a link state change from a link down to link up condition, the initiator must send an ADISC (Address Discovery) or PDISC (Port Discovery) ELS (Extended Link Service) command to every target with which it has I/O""s in progress. The ADISC and PDISC commands are used to exchange node name and port name information. The PLDA profile further requires that if the target detects that the network address of an initiator has changed, then the target should terminate the existing I/Os from that initiator. After this step, the initiator performs a recovery process and in some other way restarts the I/O transmission.
The termination of existing I/Os because of a network address change is disruptive. This termination reduces the overall performance of the network, because it unnecessarily slows system or network traffic. In some applications, such as where a tape drive serves as the target for a SCSI initiator, a general application failure may result. Moreover, loss of data results in many instances where this I/O termination process must occur.
In Fibre Channel, initiators talk to targets using network address (PID""s). These are called AL-PA""s, Arbitrated Loop Physical Address, in an arbitrated Loop environment and PID""s in other topology. Each target and each initiator is assigned a PID. In essence, targets and initiators only know one another in the Fibre Channel network by their network address.
In the event of a link state change, such as when a link goes down and then comes back up, or when a new node is added into the network, the network address of either or both the initiator or target can change. The initiator may be, for example, a host personal computer that initiates a SCSI command. A target may be some type of SCSI device such as a CD-ROM, a tape drive, or other storage device. If a state change occurs in the network while the I/Os are still in the process of being transmitted, a problem may arise upon the resumption of transmission. If a link state change occurs an address change could result. Because the initiator and target conventionally only use the addresses for identification, a confused state can arise in the I/O transmission. This confused state could have numerous manifestations, not the least of which would be the generation of corrupted data, loss of security, or generally low performance of the network.
The PLDA (Private Loop Direct Attach) Profile addresses this problem by assigning to each target and each initiator in a Fibre Channel network loop a unique node name and a unique port name, each of which are represented as 64-bit identifiers. The node name for the initiator or target defines the node for the particular device, while the port name defines the particular port on the identified node. Note, however, that a given node may possess numerous ports. Accordingly, the port name uniquely identifies the desired port on the given node.
The initiator and target exchange the node name and port name during initial communication, as defined in the FC-PH (Fibre Channel Physical) Standard. The node name and port name, when combined with the PID, uniquely identify a node. In the PLDA profile, after a link state change, the initiators send either an ADISC (Address Discovery) or PDISC (Port Discovery) command. The ADISC or PDISC command communicates between the target and initiator, the port name, node name, and PID for identification. The target and initiator compare the node name, port name, and PID, provided during initial communication to the node name, port name, and PID, provided by the ADISC or PDISC command. If they are the same, then the same target and same initiator are communicating with one another both before and after the state change. If not, then the addresses have changed.
According to the PLDA profile, the set of data including the PID, the node name, and the port name is called a xe2x80x9ctriplet.xe2x80x9d Thus, a triplet in a Fibre Channel network uniquely identifies a network node. In a Fibre Channel network, the PID is the address from which the ADISC or PDISC is received. The ADISC or PDISC, therefore, includes the port name and node name within their data payload.
The initiator sends out the ADISC or PDISC. In response, the target sends to the initiator an xe2x80x9cacceptxe2x80x9d command, which operates as essentially a xe2x80x9chandshakexe2x80x9d that includes the same information as the ADISC or PDISC command. In addition, the target sends to the initiator the target""s PID address together with the target""s port name and node name.
The handshaking occurs prior to I/O continuation between the target and initiator following a state change. Thus, every time a link goes down and then comes back up later this form of authentication occurs. Actually, authentication occurs continually throughout the communication of I/Os in the Fibre Channel arbitrated loop.
According to the PLDA profile, when I/Os are in progress and a target""s PID changes, the target is to abort all I/Os. Then, the initiator must perform error recovery on these aborted I/O""s.
Aborting I/O""s in accordance with the authentication process defined by the PLDA profile results in performance problems. In the case of SCSI tape operations the authentication process may result in application failures from which the associated host may not be able to recover. That is, in the example of a SCSI tape it may be impossible for the host to identify the physical location of the tape head or the sequentially-fed tape. Other problems arise from the present method of target authentication following a state change in the Fibre Channel network because the process is in essence a catastrophic procedure for addressing a rather common Fibre Channel network occurrence.
In a multi-initiator network, the current standard for PLDA that requires target authentication following a failure such as a tape failure cannot operate. In the event that the I/O are interrupted, all initiators on the multi-initiator network must take the time and cause the necessary delays associated with the target authentication process. Accordingly, there is a need for a method and system that addresses the performance limitations arising in the known systems and methods for identifying targets and initiators following a state change in a Fibre Channel network loop.
A need exists for a method and system that overcomes the data loss problems occurring in known target authentication methods and systems during a state change in a Fibre Channel network.
Still, a need exists for a method and system that avoids the general application failure that may happen in sequentially-operated and other target and initiator devices upon the change of state in a Fibre Channel network.
There is still the further need for a method and system for handling delays in I/Os through a multi-initiator Fibre Channel arbitrated loop network that avoids the need for each initiator to perform the target authentication process upon I/O transmission being restarted following a break in transmission.
According to the teachings of the present invention there is provided a method and system for managing I/O transmission in a Fibre Channel network that maintains target and initiator states across address changes in the Fibre Channel network to eliminate or at least substantially reduce limitations associated with known such systems and methods, including the problems of limited network performance, loss of data in certain applications, and general application failures.
One aspect of the present invention is a method for maintaining the state of a network device following a state change in a Fibre Channel network. The method includes the step of sending from a first network device a command comprising a data triplet. The data triplet comprises the network address, the node name, and the port name for the first network node. The node may represent a device such as an initiator or target in a Fibre Channel network. The Fibre Channel network may be a Fibre Channel arbitrated loop or switched network or other network topology. A next step in the method is to receive in a second network device the triplet from the first network device to determine whether the first network device and the second network device had been in I/O communication prior to the state change. The method further includes the step of determining whether the first network device and second network device were, in fact, in communication prior to the network state change by determining whether the triplet received by the second network device matches the same data (network Id, node name, and port name) existing in a prior triplet identifying the first network device prior to the network state change. In the event that the triplet matches, the method further includes the step of continuing communications. Otherwise, the method requires the termination of any interrupted I/O transmissions arising from the network state change.
According to another aspect of the present invention, there is provided a system for maintaining node states across address changes in a Fibre Channel network. The invention includes the instructions and circuitry for maintaining in each of a plurality of nodes a triplet table including at least one data triplet including for each of other ones of the plurality of nodes with which the each of said plurality of nodes communicates the physical address, node name, and port name of said other ones of said plurality of nodes. The nodes may be an initiator or target device in a Fibre Channel network. The instructions permit sending the data triplet from each of the plurality of nodes to the other ones of the plurality of nodes with which the given node communicates following the resumption of communication after a break in communication for identifying the given node in the event that the given node and the other nodes are communicating with the same ones of said each of said plurality of nodes both before and after the communications break, the process includes continuing the communication among the nodes without performing further recovery steps.
As a technical advantage, the present invention maintains initiator/target state information across address changes in a Fibre Channel network. This technical advantage is particularly valuable in the context of a network having more than one initiator. Basically, the initiator and target use the node name and port name identifiers to uniquely identify with whom they are communicating. The node name and port name are assured to be unique. In such a network, the situation of continually performing the prior art target authentication process, including the step of restarting all I/Os, can devastate the networks performance. This is because in a multi-initiator environment each individual must separately perform the target authentication process. This is not needed in networks employing the present invention.
A technical advantage that the present invention includes is providing improved multi-initiator network testing procedures. In such a network, numerous initiators often operate simultaneously or, at least, cooperatively. In these networks, frequently, maintenance of an initiator is needed for some reason or other. Taking down the initiator will generally affect not only the individual initiator, but all initiators on the network, because addresses change as a result of the removal of the initiator under maintenance. The present invention avoids the need for all initiators to perform the prior art target authentication process in this and similar instances.
Still another technical advantage appearing in the present invention relates to its ability to be made part of a Fibre Channel network with little additional cost. Generally, the method present invention may be implemented as a change in the instructions that control the authentication and transfer of triplets in a Fibre Channel network. These changes may be implemented in a hardware protocol chip for controlling the protocol operations within the network. Even this modification may be done with relatively little expense.
Another technical advantage of the present invention is the ability to restart I/O transmission immediately after completing authentication when it is confirmed that the same target and initiator are communicating with one another as were communicating prior to the I/O transmission break. Upon performing the authentication to verify the communication link, I/O transmission resumes. There is no need to perform the prior art recovery and restarting for I/O transmission.
Yet another technical advantage provided by the present invention arises from the difference of inherent paradigms used for Fibre Channel communications. Most conventional network applications use a SCSI-2 paradigm for I/O transmission. Fibre Channel applications, however, most often use the SCSI-3 paradigm. In the SCSI-3 paradigm, I/O transmission breaks occur frequently as a matter of normal operation. On the other hand, SCSI-2 paradigm operations do not normally use breaks, instead treating them as system or network failure conditions. The present invention avoids the drastic measure of recovery and restarting in response only I/O transmission breaks. This difference in SCSI-2 and SCSI-3 paradigm operations and the manner in which the present invention addresses these differences even further emphasizes the importance and relevance of its authentication method.